The present invention relates generally to indiciasensing apparatus for sensing the relative position of preprinted indicia on a moving web of material and, more particularly, to an indicia-sensing device for detecting predetermined register indicia on a moving film web having an obstructing field of indicia positioned about the register indicia.
The use of composite material in packaging applications has met with a growing acceptance in the past few years because of high strength, low cost, and other characteristics which make it superior to conventional paper board or cardboard in many applications. A typical composite may have a thin layer of plastic film adhered to a relatively thicker layer of paper board material. A method of producing such a composite material is described in U.S. Pat. No. 4,254,173 issued Mar. 3, 1981, for COMPOSITE MATERIAL FOR SECONDARY CONTAINER PACKAGING of A. Dean Peer, Jr., which is hereby incorporated for reference for all that it contains.
During high speed production of composite material such as the type described in the Peer patent, a continuously moving web of paper board material is adhered to a continuously moving web of plastic film material at a relatively high speed. During such high speed laminating operations, the relatively thin plastic web is subject to a number of conditions which may cause it to shrink or expand prior to lamination with the paper board web. Composite material used for packaging may have a repeating set of graphics printed on the plastic film web; and, thus, it is essential to control the stretch or relaxation in the plastic film web in order to provide a composite material having graphics of an exact, predetermined dimension. The method and apparatus for controlling the longitudinal dimension of each repeating set of graphics on a moving film web are described in U.S. patent application Ser. No. 441,276, now U.S. Pat. No. 4,496,417 filed Nov. 12, 1982, for CONTROL STRETCH LAMINATING DEVICE of Haake, Fowler, and Jensen, which is hereby incorporated by reference for all that it contains.
As disclosed in the Haake et al. application, an essential part of a film-stretch-control apparatus is a monitoring device which monitors the passage of certain fixed indicia on the film web which are located at a predetermined position on each repeat length of the film web. The indicia in the Haake et al. application are sensed by high speed photoelectric devices; and a monitoring signal therefrom is processed by a high speed data processing device which also receives a signal indicating the film web velocity and, from these two bits of information, computes the distance between the predetermined indicia. This information is subsequently used to relatively stretch or shrink the film prior to lamination to the paper board in order to provide a composite material having graphics of a precise size and repeat length. The indicia printed on the film web described in Haake et al. move along a photoelectric scanner path which is otherwise free of indicia which would disturb the light beam of the photoelectric scanner, i.e., there are no other indicia positioned on the web as to intersect a straight line drawn between any pair of the length-indicating indicia on the film web.
In many applications wherein a set of graphics occupies the entire width of the film web, such an unobstructed path for the photoelectric sensors cannot be provided without adding an additional width of material which must be subsequently trimmed off the composite web at a significant increase in time and expense.
Thus, it would be desirable to provide a method and apparatus for detecting predetermined indicia within an obstructed field of indicia on a moving film web in order to monitor film web distortion or to provide other data relating to the moving film web. Such apparatus might be used in a similar fashion in any application wherein the recording or registering of predetermined indicia on a moving web is desired and wherein the predetermined indicia are positioned within an obstructing field of indicia.